On Tue, May 6, 2014 at 7:40 PM, Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Fri, Apr 18, 2014 at 02:44:04PM -0400, Trond Myklebust wrote:
>> state_lock is a heavily contended global lock. We don't want to grab
>> that while simultaneously holding the inode->i_lock
>> Instead do the list manipulations from the work queue context prior to
>> starting the rpc call.
>>
>> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>> ---
>> fs/nfsd/nfs4callback.c | 18 ++++++++++++++++--
>> fs/nfsd/nfs4state.c | 25 +++++++++++++++----------
>> fs/nfsd/state.h | 1 +
>> 3 files changed, 32 insertions(+), 12 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
>> index 39c8ef875f91..8626cd6af4d1 100644
>> --- a/fs/nfsd/nfs4callback.c
>> +++ b/fs/nfsd/nfs4callback.c
>> @@ -1009,9 +1009,8 @@ static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
>> run_nfsd4_cb(cb);
>> }
>>
>> -static void nfsd4_do_callback_rpc(struct work_struct *w)
>> +static void nfsd4_run_callback_rpc(struct nfsd4_callback *cb)
>> {
>> - struct nfsd4_callback *cb = container_of(w, struct nfsd4_callback, cb_work);
>> struct nfs4_client *clp = cb->cb_clp;
>> struct rpc_clnt *clnt;
>>
>> @@ -1029,11 +1028,25 @@ static void nfsd4_do_callback_rpc(struct work_struct *w)
>> cb->cb_ops, cb);
>> }
>>
>> +static void nfsd4_do_callback_rpc(struct work_struct *w)
>> +{
>> + struct nfsd4_callback *cb = container_of(w, struct nfsd4_callback, cb_work);
>> + nfsd4_run_callback_rpc(cb);
>> +}
>> +
>> void nfsd4_init_callback(struct nfsd4_callback *cb)
>> {
>> INIT_WORK(&cb->cb_work, nfsd4_do_callback_rpc);
>> }
>>
>> +static void nfsd4_do_cb_recall(struct work_struct *w)
>> +{
>> + struct nfsd4_callback *cb = container_of(w, struct nfsd4_callback, cb_work);
>> +
>> + nfsd4_prepare_cb_recall(cb->cb_op);
>> + nfsd4_run_callback_rpc(cb);
>> +}
>> +
>> void nfsd4_cb_recall(struct nfs4_delegation *dp)
>> {
>> struct nfsd4_callback *cb = &dp->dl_recall;
>> @@ -1050,6 +1063,7 @@ void nfsd4_cb_recall(struct nfs4_delegation *dp)
>>
>> INIT_LIST_HEAD(&cb->cb_per_client);
>> cb->cb_done = true;
>> + INIT_WORK(&cb->cb_work, nfsd4_do_cb_recall);
>>
>> run_nfsd4_cb(&dp->dl_recall);
>> }
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 6d691aa2bb27..85fcbc9ebd40 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -2743,24 +2743,31 @@ out:
>> return ret;
>> }
>>
>> -static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
>> +void nfsd4_prepare_cb_recall(struct nfs4_delegation *dp)
>> {
>> struct nfs4_client *clp = dp->dl_stid.sc_client;
>> struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
>>
>> - lockdep_assert_held(&state_lock);
>> + /*
>> + * We can't do this in nfsd_break_deleg_cb because it is
>> + * already holding inode->i_lock
>> + */
>> + spin_lock(&state_lock);
>> + if (list_empty(&dp->dl_recall_lru)) {
>> + dp->dl_time = get_seconds();
>> + list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
>> + }
>> + spin_unlock(&state_lock);
>> +}
>> +
>> +static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
>> +{
>> /* We're assuming the state code never drops its reference
>> * without first removing the lease. Since we're in this lease
>> * callback (and since the lease code is serialized by the kernel
>> * lock) we know the server hasn't removed the lease yet, we know
>> * it's safe to take a reference: */
>> atomic_inc(&dp->dl_count);
>> -
>> - list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
>> -
>> - /* Only place dl_time is set; protected by i_lock: */
>> - dp->dl_time = get_seconds();
>> -
>> nfsd4_cb_recall(dp);
>> }
>>
>> @@ -2785,11 +2792,9 @@ static void nfsd_break_deleg_cb(struct file_lock *fl)
>> */
>> fl->fl_break_time = 0;
>>
>> - spin_lock(&state_lock);
>> fp->fi_had_conflict = true;
>> list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
>> nfsd_break_one_deleg(dp);
>> - spin_unlock(&state_lock);
>
> Why do we know it's safe to traverse this list without holding
> state_lock?
We're in a callback that is already holding the inode->i_lock, and so
this is why we need to involve inode->i_lock when hashing/unhashing
the delegation.
> --b.
>
>> }
>>
>> static
>> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
>> index 1aa22f39fc65..02c5a203c738 100644
>> --- a/fs/nfsd/state.h
>> +++ b/fs/nfsd/state.h
>> @@ -473,6 +473,7 @@ extern void nfsd4_cb_recall(struct nfs4_delegation *dp);
>> extern int nfsd4_create_callback_queue(void);
>> extern void nfsd4_destroy_callback_queue(void);
>> extern void nfsd4_shutdown_callback(struct nfs4_client *);
>> +extern void nfsd4_prepare_cb_recall(struct nfs4_delegation *dp);
>> extern void nfs4_put_delegation(struct nfs4_delegation *dp);
>> extern struct nfs4_client_reclaim *nfs4_client_to_reclaim(const char *name,
>> struct nfsd_net *nn);
>> --
>> 1.9.0
>>
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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